/usr/lib/mono/compat-2.0/System.Web.Mvc.dll is in libmono-system-web-mvc1.0-cil 3.2.8+dfsg-10.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/lib/mono/compat-2.0/../gac/System.Web.Mvc/1.0.0.0__31bf3856ad364e35/System.Web.Mvc.dll